Bottomed container and method for manufacturing the same

ABSTRACT

A method includes a main forming step in which a blank in which creases are formed by a preforming step is set between a die and a punch such that the die and the punch correspond to the shape of the blank, and is press-formed to form a square tubular component as a bottomed container. When, in the main forming step, a rib protruding outward from between each adjacent two of the vertical walls of the bottomed container in plan view is formed in press forming, a slit is provided in each of the corner portions of the inner side surface of the die.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a bottomed container that is formed from a blank by press forming and that has a large forming height, and to a method for manufacturing the same.

2. Description of the Related Art

A fuel tank, a battery tray, and the like mounted on a vehicle are often bottomed, substantially circular tubular or square tubular components formed from a plate material by press deep drawing forming. Such a fuel tank, such a battery tray, and the like are required to have a watertight structure, and are therefore integrally formed by press forming. In addition, they are desired to have as large an internal capacity as possible, and are therefore desired to have as small a corner R in plan view as possible, and as large a forming height as possible.

However, there is a problem in that in the press deep drawing forming, the smaller the corner R, and the larger the forming height, the more easily a rupture occurs, and the more difficult the forming.

As a technique to solve such a problem, there has been proposed a technique that reduces the drawing resistance and improves the forming limit (see, for example, Japanese Patent No. 4985909). This technique holds a material with a blank holder and a die, provides a recess in part of the die, actively generates a crease in this part, thereby forms a folded flange, reduces the drawing resistance of a flange in a corner portion, and thereby improves the forming limit.

As another technique to solve the above problem, there has been proposed a forming method that forms a pair of folded flanges folded into the inside of a corner portion of a tubular component without using a blank holder (see, for example, Japanese Patent No. 3454656). This technique can perform manufacture by bending forming almost without drawing forming, and therefore promises significant improvement of forming limit.

However, the technique disclosed in Japanese Patent No. 4985909 has a problem in that because forming is performed by deep drawing forming, there is a limit on reduction of drawing resistance, and when forming a very deep product (that is, a product having a large forming height), a rupture occurs.

The art disclosed in Japanese Patent No. 3454656 has a problem in that in order to form a pair of folded flanges folded into the inside of a corner portion, a die and a punch need to be provided with a pair of special machined parts, that is, a die needs to be provided with a special guide protrusion, and a punch needs to be provided with a clearance groove corresponding thereto. In addition, a blank itself has no guide serving as a starting point of bending forming for forming a pair of folded flanges, in an area that will become a corner portion after completion of press forming, and therefore, large bending resistance is generated in the blank itself. A configuration based on such a principle has a problem in that, in press forming, it is difficult in terms of shape to prepare a pair of a die and a punch for forming two or more pairs of folded flanges in a corner portion, and in addition, the forming itself of folded flanges is unstable.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a bottomed container having a large forming height and a method for manufacturing the same in which a die and a punch need not be provided with a pair of special machined parts, and in addition, a bottomed container can be formed from a blank using cold press forming, by which mass production is possible, substantially only by bending forming.

According to a first aspect of the present invention, a bottomed container includes a bottom portion, and a plurality of vertical walls rising from the peripheral edge of the bottom portion. The bottomed container is formed by press-forming a blank, and has a plurality of corner portions integral with the bottom portion and the vertical walls adjacent to each other. The corner portions are each provided with one or more ribs that protrude outward or inward from between the vertical walls adjacent to each other in plan view. The ribs are each composed of a pair of folded flanges that are folded along creases that are preformed in the blank so as to substantially equally divide an area that will become one of the corner portions. The amount of outward or inward protrusion of the ribs becomes larger from the bottom portion toward the open end of the vertical walls in side view. The ribs are provided with no flanges extending outward from the open ends of the ribs in plan view.

According to a second aspect of the present invention, in the first aspect of the present invention, the corner portions have a substantially arc shape in plan view, and the one or more ribs formed in each of the corner portions having a substantially arc shape are two to four ribs. Here, a substantially arc shape means a curved surface shape having a constant radius of curvature, a curved surface such that straight line parts are connected together, or a polygonal shape close to a curved surface. The ribs are formed so as to protrude from corner portions having such a substantially arc shape.

According to a third aspect of the present invention, in the second aspect of the present invention, recesses or protrusions that are continuous in plan view and that correspond to the ribs protruding outward or inward from the corner portions having a substantially arc shape are formed in the bottom portion. The definition of the substantially arc shape is as described above.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the recesses or protrusions provided in the bottom portion are formed so as to extend radially from the center of each of the corner portions having a substantially arc shape in plan view. The definition of the substantially arc shape is as described above.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects of the present invention, the bottomed container is provided with flanges extending outward from the open ends of the vertical walls.

According to a sixth aspect of the present invention, a method for manufacturing the bottomed container according to the first aspect of the present invention includes a preforming step in which creases are formed in a blank having areas that will become the bottom portion, the plurality of vertical walls, and the plurality of corner portions of the bottomed container after press forming using a preforming die, the creases being formed at borders between an area that will become the bottom portion and areas that will become the vertical walls, borders between the areas that will become the vertical walls and areas that will become the corner portions, and positions for substantially equally dividing the areas that will become the corner portions, and a main forming step in which the blank in which creases are formed by the preforming step is set between a die and a punch such that the die and the punch correspond to the shape of the blank, and is press-formed to form the bottomed container. In the main forming step, when one or more ribs protruding outward from between each adjacent two of the vertical walls of the bottomed container in plan view are formed in press forming, slits are provided in corner portions of the die, and when one or more ribs protruding inward from between each adjacent two of the vertical walls of the bottomed container in plan view are formed in press forming, slits are provided in corner portions of the outer side surface of the punch.

According to a seventh aspect of the present invention, in the sixth aspect of the present invention, in the preforming step, the number of creases formed for substantially equally dividing each of the areas that will become the corner portions is three to seven.

According to an eighth aspect of the present invention, in the sixth or seventh aspect of the present invention, the inside of each of the corner portions of the die is formed such that the radius of curvature of the inscribed circle is R1 in plan view, the corner portions of the outer side surface of the punch are formed in a shape having a curved surface having a radius of curvature of R2 in plan view corresponding to the inscribed circle of each of the corner portions of the die, the clearance between the punch and the die defined as R1−R2 is set to 100% to 200% of the thickness of the blank, and R1>R2.

According to a ninth aspect of the present invention, in the eighth aspect of the present invention, in the main forming step, when one or more ribs protruding outward from between each adjacent two of the vertical walls of the bottomed container in plan view are formed in press forming, slits are provided in the corner portions of the bottom surface of the die, and when one or more ribs protruding inward from between each adjacent two of the vertical walls of the bottomed container in plan view are formed in press forming, slits are provided in the corner portions of the bottom surface of the punch.

According to a tenth aspect of the present invention, in the ninth aspect of the present invention, the slits provided in the corner portions of the bottom surface of the die or the corner portions of the bottom surface of the punch are formed so as to extend radially from the center of each corner portion.

According to an eleventh aspect of the present invention, in any one of the sixth to tenth aspect of the present invention, flanges extending outward from the outer side surface other than the corner portions of the punch are provided at the upper end of the punch.

As described above, a bottomed container of the present invention includes a bottom portion, and a plurality of vertical walls rising from the peripheral edge of the bottom portion. The bottomed container is formed by press-forming a blank, and has a plurality of corner portions integral with the bottom portion and the vertical walls adjacent to each other. The corner portions are each provided with one or more ribs that protrude outward or inward from between the vertical walls adjacent to each other in plan view. The ribs are each composed of a pair of folded flanges that are folded along creases that are preformed in the blank so as to substantially equally divide an area that will become one of the corner portions. The amount of outward or inward protrusion of the ribs becomes larger from the bottom portion toward the open end of the vertical walls in side view. The ribs are provided with no flanges extending outward from the open ends of the ribs in plan view. Therefore, a die and a punch need not be provided with a pair of special machined parts, and in addition, a bottomed container having a large forming height can be formed from a blank using cold press forming, by which mass production is possible, substantially only by bending forming.

A method for manufacturing a bottomed container of the present invention includes a preforming step in which creases are formed in a blank having areas that will become the bottom portion, the plurality of vertical walls, and the plurality of corner portions of the bottomed container after press forming using a preforming die, the creases being formed at borders between an area that will become the bottom portion and areas that will become the vertical walls, borders between the areas that will become the vertical walls and areas that will become the corner portions, and positions for substantially equally dividing the areas that will become the corner portions, and a main forming step in which the blank in which creases are formed by the preforming step is set between a die and a punch such that the die and the punch correspond to the shape of the blank, and is press-formed to form the bottomed container. In the main forming step, when one or more ribs protruding outward from between each adjacent two of the vertical walls of the bottomed container in plan view are formed in press forming, slits are provided in corner portions of the die, and when one or more ribs protruding inward from between each adjacent two of the vertical walls of the bottomed container in plan view are formed in press forming, slits are provided in corner portions of the outer side surface of the punch. Therefore, a manufacturing method in which a die and a punch need not be provided with a pair of special machined parts, and in addition, a bottomed container can be formed from a blank using cold press forming, by which mass production is possible, substantially only by bending forming, can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view illustrating a blank before being formed into a bottomed container of Embodiment 1 of the present invention;

FIG. 2 is a partial enlarged perspective view of a preforming die according to Embodiment 1;

FIGS. 3A and 3B are partial enlarged views of the blank before and after preforming according to Embodiment 1, FIG. 3A is an enlarged view of part IIIA before preforming shown in FIG. 1, and FIG. 3B is a perspective view after preforming;

FIG. 4 is a schematic perspective view showing the positional relationship between a punch, the blank after preforming, and a die in main forming according to Embodiment 1;

FIGS. 5A and 5B show the shape and dimensions of the punch and die shown in FIG. 4;

FIGS. 6A to 6D show the transformation state of the blank during main forming according to Embodiment 1;

FIG. 7 is a schematic plan view illustrating a blank before being formed into a bottomed container of Embodiment 2 of the present invention;

FIG. 8 is a partial enlarged perspective view of a preforming die according to Embodiment 2;

FIGS. 9A and 9B are partial enlarged views of the blank before and after preforming according to Embodiment 2, FIG. 9A is an enlarged view of part IXA before preforming shown in FIG. 7, and FIG. 9B is a perspective view after preforming;

FIG. 10 is a schematic perspective view showing the positional relationship between a punch, the blank after preforming, and a die in main forming according to Embodiment 2;

FIGS. 11A to 11D show the transformation state of the blank during main forming according to Embodiment 2;

FIG. 12 is a schematic plan view illustrating a blank before being formed into a bottomed container of Embodiment 3 of the present invention;

FIG. 13 is a partial enlarged perspective view of a preforming die according to Embodiment 3;

FIGS. 14A and 14B are partial enlarged views of the blank before and after preforming according to Embodiment 3, FIG. 14A is an enlarged view of part XIVA before preforming shown in FIG. 12, and FIG. 14B is a perspective view after preforming;

FIG. 15 is a schematic perspective view showing the positional relationship between a punch, the blank after preforming, and a die in main forming according to Embodiment 3;

FIGS. 16A and 16B show the shape and dimensions of the punch and die shown in FIG. 15; and

FIGS. 17A to 17E show the transformation state of the blank during main forming according to Embodiment 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described in detail.

Embodiment 1

FIG. 1 is a schematic plan view illustrating a blank before being formed into a bottomed container of Embodiment 1 of the present invention. FIG. 2 is a partial enlarged perspective view of a preforming die according to Embodiment 1. FIGS. 3A and 3B are partial enlarged views of the blank before and after preforming according to Embodiment 1, FIG. 3A is an enlarged view of part IIIA before preforming shown in FIG. 1, and FIG. 3B is a perspective view of part IIIA after preforming. FIG. 4 is a schematic perspective view showing the positional relationship between a punch, the blank after preforming, and a die in main forming according to Embodiment 1. FIGS. 5A and 5B show the shape and dimensions of the punch and die shown in FIG. 4. FIGS. 6A to 6D show the transformation state of the blank during main forming according to Embodiment 1.

In FIG. 1, reference sign 1 denotes a blank 800 mm by 1000 mm and 1.0 mm thick made of 6000 series aluminum alloy before cold press forming (hereinafter also simply referred to as “press forming”), reference sign 1 a denotes an area that will become a bottom portion of a square tubular component as a bottomed container after press forming, reference sign 1 b denotes areas that will become a plurality of (four) vertical walls of the square tubular component after press forming, and reference sign 1 c denotes areas that will become a plurality of (four) corner portions of the square tubular component after press forming.

FIG. 2 shows a preforming die 2 for forming creases (for detail, see FIG. 3B described later) in the blank 1 having the areas 1 a, 1 b, and 1 c shown in FIG. 1, the creases being formed at the borders between the area 1 a that will become the bottom portion and the areas 1 b that will become the vertical walls, the borders between the areas 1 b that will become the vertical walls and the areas 1 c that will become the corner portions, and positions that substantially equally divide (into two halves) the areas 1 c that will become the corner portions. In FIG. 2, reference sign 2 a denotes an area of the preforming die 2 corresponding to the area 1 a that will become the bottom portion, reference sign 2 b denotes areas of the preforming die 2 corresponding to the areas 1 b that will become the vertical walls, and reference sign 2 c denotes areas of the preforming die 2 corresponding to the areas 1 c that will become the corner portions.

FIG. 3A is an enlarged view of part IIIA of the blank 1 before preforming shown in FIG. 1. FIG. 3B is a perspective view of part IIIA of the blank 1 after creases 1 d, 1 e, and if are formed (preforming step) in the blank 1 shown in FIG. 1 using the preforming die 2 shown in FIG. 2, the creases being formed at the borders between the area 1 a that will become the bottom portion and the areas 1 b that will become the vertical walls, the borders between the areas 1 b that will become the vertical walls and the areas 1 c that will become the corner portions, and positions that substantially equally divide (into two halves) the areas 1 c that will become the corner portions.

FIG. 4 is a schematic perspective view showing the positional relationship between a punch 3, the blank 1 after preforming, and a die 4 in main forming according to Embodiment 1.

In FIG. 4, the blank 1 in which creases 1 d, 1 e, and 1 f are formed by the above-described preforming step is set between a die 4 (for detail, see FIG. 5B described later) and a punch 3 (for detail, see FIG. 5A described later) such that the die 4 and the punch 3 correspond to the shape of the blank 1, and is press-formed to form a square tubular component as a bottomed container (main forming step). In this main forming step, a blank holder need not be used.

The die 4 shown in FIG. 4 is provided with a bottom surface 4 a, inner side surfaces 4 b, and corner portions 4 c respectively corresponding to the area 1 a that will become a bottom portion, the areas 1 b that will become vertical walls, and the areas 1 c that will become corner portions, of the blank 1. The corner portions 4 c of the die 4 are each provided with a slit 4 f that is used when a rib 1 g (see FIG. 6D described later) that protrudes outward from between each adjacent two of the vertical walls 1 b of the square tubular component in plan view is formed during press forming.

The transformation state of the blank 1 after preforming in the case where the above-described main forming step was performed on the basis of the blank 1 having creases 1 d, 1 e, and 1 f formed by the above-described preforming step, the detailed shapes of the punch 3 and the die 4 shown in FIGS. 5A and 5B, the clearance between the punch 3 and the die 4 (the thickness of the blank 1 (1 mm)+(20% of the thickness of the blank 1 (1 mm)=0.2 mm)=1.2 mm), and lubricant (wash oil for steel plate is assumed) and coefficient of friction μ=0.14, was calculated using general-purpose dynamic explicit method software PAM-STAMP (calculation result is shown in FIGS. 6A to 6D as deformation state diagrams). The calculation model was in ¼ symmetric condition.

FIGS. 6A to 6D are transformation state diagrams showing the above-described calculation result. FIGS. 6A, 6B, 6C, and 6D respectively show the transformation state of the blank 1 after preforming at a position 70 mm above the bottom dead center (BDC) (at which the punch 3 is in its lowest position) (hereinafter referred to as BDC 70 mm UP), BDC 50 mm UP, BDC 20 mm UP, and BDC. From this, it can be seen that the main forming step progresses stably. In FIG. 6D, it can be seen that a rib 1 g composed of a pair of folded flanges that protrude outward from between each adjacent two of the vertical walls 1 b of the square tubular component is formed excellently in each corner portion 1 c. That is, a square tubular component can be formed only by bending without drawing the corner portions 1 c. For this reason, if the height of the square tubular component is increased, the drawing resistance to the blank 1 does not increase. In other words, a square tubular component (bottomed container) that is free from rupture can be obtained without increasing the amount of strain in each parts. This rib 1 g becomes larger from the bottom portion 1 a toward the open ends of the vertical walls 1 b in side view, and the rib 1 g is provided with no flanges extending outward from the open end of the rib 1 g in plan view.

Although, in Embodiment 1, an example in which a rib 1 g protruding outward from between each adjacent two of the vertical walls 1 b of the square tubular component is formed in each corner portion 1 c has been described, the present invention is not limited to this. For example, when a rib protruding inward from between each adjacent two of the vertical walls 1 b of the square tubular component is formed in each corner portion 1 c, a slit may be provided in each corner portion of the outer side surface of the punch 3. Although, in Embodiment 1, an example in which a square tubular component is formed as a bottomed container has been described, the present invention is not limited to this. The present invention can be widely applied, for example, to a triangular tubular component, and a five or more-sided polygonal tubular component. Although, in Embodiment 1, an example in which a rib 1 g protruding outward from between each adjacent two of the vertical walls 1 b in plan view is formed in each corner portion 1 c has been described, the present invention is not limited to this. For example, two or more ribs 1 g that protrude outward or inward from between each adjacent two of the vertical walls 1 b in plan view may be provided in each corner portion 1 c (for details, see Embodiments 2 and 3 described later). Although, in Embodiment 1, an example in which a blank 1 is made of 6000 series aluminum alloy has been described, the present invention is not limited to this. For example, a blank 1 may be made of an aluminum alloy other than 6000 series, a titanium alloy, which is a material difficult to machine, or an ordinary steel. The advantage that this rib 1 g serves as a reinforcing part resisting against bending deformation of each corner portion 1 c can also be obtained.

As described above, use of the configuration of the present invention not only eliminates the need to provide a die and a punch with a pair of special machined parts, but also makes it possible to form a bottomed container having a large forming height from a blank using cold press forming, by which mass production is possible, substantially only by bending forming.

Embodiment 2

FIG. 7 is a schematic plan view illustrating a blank before being formed into a bottomed container of Embodiment 2 of the present invention. FIG. 8 is a partial enlarged perspective view of a preforming die according to Embodiment 2. FIGS. 9A and 9B are partial enlarged views of the blank before and after preforming according to Embodiment 2, FIG. 9A is an enlarged view of part IXA before preforming shown in FIG. 7, and FIG. 9B is a perspective view after preforming. FIG. 10 is a schematic perspective view showing the positional relationship between a punch, the blank after preforming, and a die in main forming according to Embodiment 2. FIGS. 11A to 11D show the transformation state of the blank during main forming according to Embodiment 2. In this embodiment, the same reference signs will be used to designate the same components as those of Embodiment 1, detailed description thereof will be omitted, and only differences will be described in detail.

In FIG. 7, the blank 1 is formed in a shape based on the premise that two ribs are formed in each of the areas 1 c that will become corner portions. That is, the blank 1 is formed in such a shape that vertical walls 1 b are equal in height to two ribs in side view after main forming (press forming) (see FIG. 9A).

FIG. 8 shows a preforming die 5 for forming creases (for detail, see FIG. 9R described later) in the blank 1 having the areas 1 a, 1 b, and 1 c, shown in FIG. 7, the creases being formed at the borders between the area 1 a that will become the bottom portion and the areas 1 b that will become the vertical walls, the borders between the areas 1 b that will become the vertical walls and the areas 1 c that will become the corner portions, and positions that substantially equally divide (into four parts) the areas 1 c that will become the corner portions. In FIG. 8, reference sign 5 a denotes an area of the preforming die 5 corresponding to the area 1 a that will become the bottom portion, reference sign 5 b denotes areas of the preforming die 5 corresponding to the areas 1 b that will become the vertical walls, and reference sign 5 c denotes areas of the preforming die 5 corresponding to the areas 1 c that will become the corner portions.

FIG. 10 is a schematic perspective view showing the positional relationship between a punch 3, the blank 1 after preforming, and a die 4 in main forming according to Embodiment 2.

In FIG. 10, the blank 1 in which a crease 1 d, a crease 1 e, and three creases 1 f are formed by the above-described preforming step is set between a die 4 and a punch 3 such that the die 4 and the punch 3 correspond to the shape of the blank 1, and is press-formed to form a square tubular component as a bottomed container (main forming step). In this main forming step, a blank holder need not be used.

The corner portions 4 c of the die 4 shown in FIG. 10 are each provided with two slits 4 f that are used when two ribs 1 g (see FIG. 11D described later) that protrude outward from between each adjacent two of the vertical walls 1 b of the square tubular component in plan view are formed during press forming.

The transformation state of the blank 1 after preforming in the case where the above-described main forming step was performed on the basis of the blank 1 having a crease 1 d, a crease 1 e, and three creases 1 f formed by the above-described preforming step, the punch 3 and the die 4 shown in FIG. 10, the clearance between the punch 3 and the die 4 (the thickness of the blank 1 (1 mm)+(20% of the thickness of the blank 1 (1 mm)=0.2 mm)=1.2 mm), lubricant (wash oil for steel plate is assumed) and coefficient of friction μ=0.14, was calculated using general-purpose dynamic explicit method software PAM-STAMP (calculation result, is shown in FIGS. 11A to 11D as deformation state diagrams). The calculation model was in ¼ symmetric condition.

FIGS. 11A to 11D are transformation state diagrams showing the above-described calculation result. FIGS. 11A, 11B, 11C, and 11D respectively show the transformation state of the blank 1 after preforming at BDC 70 mm UP, BDC 50 mm UP, RDC 20 mm UP, and BDC. From this, it can be seen that the main forming step progresses stably. Tn FIG. 11D, it can be seen that two ribs 1 g each composed of a pair of folded flanges that protrude outward from between adjacent vertical walls 1 b of the square tubular component are formed excellently in the corner portion 1 c. That is, a square tubular component can be formed only by bending without drawing the corner portions 1 c. For this reason, if the height of the square tubular component is increased, the drawing resistance to the blank 1 does not increase. In other words, a square tubular component (bottomed container) that is free from rupture can be obtained without increasing the amount of strain in each parts. However, in the case of Embodiment 2, a punch 3 and a die 4 that have a very small corner R in plan view are provided with a plurality of ribs 1 g, and therefore the clearance between the punch 3 and die 4 is large in the slits 4 f in each corner portion 4 c of the die 4. For this reason, there is a problem in that the shape of ribs 1 g after press forming is not formed as sharp as the shape of Embodiment 1. When it is desired to form such ribs 1 g more sharply, the corner R needs to be set slightly larger according to the number of the ribs 1 g as in Embodiment 3 described later. The two ribs 1 g become larger from the bottom portion 1 a toward the open ends of the vertical walls 1 b in side view, and the two ribs 1 g are provided with no flanges extending outward from the open ends of the ribs 1 g in plan view.

When two ribs 1 g are provided in each corner portion 1 c as in Embodiment 2, the amount of protrusion of the ribs 1 g can be reduced compared to the case where two ribs 1 g are provided in each corner portion 1 c as in Embodiment 1. Therefore, the number of ribs 1 g provided in each corner portion 1 c is preferably two or more. However, if the number of ribs 1 g provided in each corner portion 1 c is increased as described above, ends of slits 4 f facing the inside of each corner portion 4 c of die 4 overlap. In such a part, the clearance between the punch 3 and the die 4 is large, and therefore the shape of ribs 1 g is not formed stably. If the width of the slits 4 f is reduced so that the ends of the slits 4 f do not overlap, the volume of the part subjected to deformation load is also reduced, and it is a challenge to secure the strength of the die 4. In order to secure a certain width of the slits 4 f and to form a necessary number of relatively sharp ribs 1 g, the radius of curvature R of corner portions 4 c needs to be set, larger according to the number of the ribs 1 g. That is, if the number of ribs 1 g is too small, the amount, of protrusion of ribs 1 g into or out of each corner portion 1 c is large, and if the number of ribs 1 g is too large, the radius of curvature R of corner portions 4 c in plan view is large. From the viewpoint of shape limitation and securing of internal capacity, a square tubular component (bottomed container) that has a relatively small corner R (the radius of curvature R is about 80 mm or less) and in which the amount of protrusion of ribs 1 g out of or into the production is small, is desired. In order to obtain such a square tubular component (bottomed container), the number of ribs 1 g provided in each corner portion 1 c is preferably four or less.

As described above, use of the configuration of the present invention not only eliminates the need to provide a die and a punch with a pair of special machined parts, but also makes it possible to form a bottomed container having a large forming height from a blank using cold press forming, by which mass production is possible, substantially only by bending forming.

Embodiment 3

FIG. 12 is a schematic plan view illustrating a blank before being formed into a bottomed container of Embodiment 3 of the present invention. FIG. 13 is a partial enlarged perspective view of a preforming die according to Embodiment 3. FIGS. 14A and 14B are partial enlarged views of the blank before and after preforming according to Embodiment 3, FIG. 14A is an enlarged view of part XIVA before preforming shown in FIG. 12, and FIG. 14B is a perspective view after preforming. FIG. 15 is a schematic perspective view showing the positional relationship between a punch, the blank after preforming, and a die in main forming according to Embodiment 3. FIGS. 16A and 16B show the shape and dimensions of the punch and die shown in FIG. 15. FIGS. 17A to 17E show the transformation state of the blank during main forming according to Embodiment 3. In this embodiment, the same reference signs will be used to designate the same components as those of Embodiments 1 and 2, detailed description thereof will be omitted, and only differences will be described in detail.

In FIG. 12, the blank 1 is formed in a shape based on the premise that four ribs are formed in each of the areas 1 c that will become a corner portions. That is, the blank 1 is formed in such a shape that vertical walls 1 b are equal in height to four ribs in side view after main forming (press forming) (see FIG. 14A).

FIG. 13 shows a preforming die 6 for forming creases (for detail, see FIG. 14B described later) in the blank 1 having the areas 1 a, 1 b, and 1 c shown in FIG. 12, the creases being formed at the borders between the area 1 a that will become the bottom portion and the areas 1 b that will become the vertical walls, the borders between the areas 1 b that will become the vertical walls and the areas 1 c that will become the corner portions, and positions that divide equally (into eight parts) the areas 1 c that will become the corner portions. In FIG. 13, reference sign 6 a denotes an area of the preforming die 6 corresponding to the area 1 a that will become the bottom portion, reference sign 6 b denotes areas of the preforming die 6 corresponding to the areas 1 b that will become the vertical walls, and reference sign 6 c denotes areas of the preforming die 6 corresponding to the areas 1 c that will become the corner portions.

FIG. 15 is a schematic perspective view showing the positional relationship between a punch 7, the blank 1 after preforming, and a die 8 in main forming according to Embodiment 3.

In FIG. 15, the blank 1 in which a crease 1 d, a crease 1 e, and seven creases 1 f are formed by the above-described preforming step is set between a die 8 (for detail, see FIG. 16B described later) and a punch 7 (for detail, see FIG. 16A described later) such that the die 8 and the punch 7 correspond to the shape of the blank 1, and is press-formed to form a square tubular component as a bottomed container (main forming step). In this main forming step, a blank holder need not be used.

The inside of each corner portion 8 c of the die 8 shown in FIG. 16B is formed such that the radius of curvature R1 of the inscribed circle is 66.9 mm. The corner portions 8 c are further provided with four slits 8 f that are used when four ribs 1 g (see FIG. 17E described later) that protrudes outward from between adjacent vertical walls 1 b of the square tubular component in plan view is formed during press forming. The corner portions 7 c of the outer side surface of punch 7 are formed in a shape having a curved surface having a radius of curvature R2 of 65.7 mm in plan view corresponding to the inscribed circle of each corner portion 8 c of the die 8. Here, R1>R2. The clearance between punch 7 and die 8 defined as the difference between the radius of curvature R1 of the inscribed circle and the radius of curvature R2 is 1.2 mm. In the main forming step, a bottomed container is formed without drawing forming, only by bending forming, and therefore, the change in thickness of blank 1 is very small. For this reason, the above-described clearance can be up to about 100% of the thickness of blank 1. If the clearance is too large, the shape of ribs 1 g is not formed sharply, and therefore, it can be said that the clearance is preferably at most 200% (of the thickness of the blank 1). As described above, in the case of a bottomed container formed by the main forming step, the change in thickness of blank 1 as a material is very small compared to the case of an ordinary drawn component. That is, in the case of ordinary drawing forming, the thickness of the blank 1 decreases in the vicinity of the shoulder R of the punch 7 and increases on the shoulder R side of the die 8 owing to inflow of material. If the product performance is designed based on the vicinity of the shoulder R where local reduction in thickness occurs, the weight of the formed component increases slightly. A manufacturing method including the main forming step has the advantage that the change in thickness of the blank 1 associated with forming is small, and therefore, compared to the above-described drawing forming, the product is lightweight, and the strength and rigidity of the product can be secured.

The transformation state of the blank 1 after preforming in the case where the above-described main forming step was performed on the basis of the blank 1 in which a crease 1 d, a crease 1 e, and seven creases 1 f were formed by the above-described preforming step, the punch 7 and the die 8 shown in FIG. 15, the clearance between the punch 7 and the die 8 (the thickness of the blank 1 (1 mm)+(20% of the thickness of the blank 1 (1 mm)=0.2 mm)=1.2 mm), lubricant (wash oil for steel plate is assumed) and coefficient of friction μ=0.14, was calculated using general-purpose dynamic explicit method software PAM-STAMP (calculation result is shown in FIGS. 17A to 17E as deformation state diagrams). The calculation model was in ¼ symmetric condition.

FIGS. 17A to 17E are transformation state diagrams showing the above-described calculation result. FIGS. 17A, 17B, 17C, 17D, and 17E respectively show the transformation state of the blank 1 after preforming at BDC 70 mm UP, BDC 50 mm UP, BDC 20 mm UP, BDC 10 mm UP, and BDC. From this, it can be seen that the main forming step progresses further stably compared to Embodiments 1 and 2. In FIG. 17E, it can be seen that four ribs 1 g each composed of a pair of folded flanges that protrude outward from between adjacent vertical walls 1 b of the square tubular component are formed excellently in the corner portion 1 c. That is, a square tubular component can be formed more easily only by bending without drawing the corner portions 1 c. For this reason, if the height of the square tubular component is increased, the drawing resistance to the blank 1 does not increase. In other words, a square tubular component (bottomed container) that is free from rupture can be obtained without increasing the amount of strain in each parts. The four ribs 1 g become larger from the bottom portion 1 a toward the open ends of the vertical walls 1 b in side view, and the four ribs 1 g are provided with no flanges extending outward from the open ends of the ribs 1 g in plan view.

When four ribs 1 g are provided in each corner portion 1 c as in Embodiment 3, the amount of protrusion of ribs 1 g is small compared to Embodiment 2. The strength of corner portions 1 c of Embodiment 3 is high compared to Embodiment 2.

As described above, use of the configuration of the present invention not only eliminates the need to provide a die and a punch with a pair of special machined parts, but also makes it possible to form a bottomed container having a large forming height from a blank using cold press forming, by which mass production is possible, substantially only by bending forming.

In the main forming step of Embodiment 3, providing slits in corner portions of bottom surface 8 a of die 8 when one or more ribs 1 g protruding outward from between adjacent vertical walls 1 b of square tubular component (bottomed container) in plan view in press forming, or providing slits in corner portions of bottom surface of punch 7 when one or more ribs 1 g protruding inward from between adjacent vertical walls 1 b of square tubular component (bottomed container) in plan view in press forming, makes it easier and more stable to form a square tubular component (bottomed container).

Forming slits provided in the corner portions 8 c of the bottom surface 8 a of the die 8 or the corner portions of the bottom surface of the punch 7 such that the slits extend radially from the center of each corner portion makes the forming positions of the ribs 1 g more stable, and makes it much easier and much more stable to form a square tubular component (bottomed container).

By providing flanges (not shown) extending outward from the outer side surface other than the corner portions 7 c of punch 7 on the upper end of the punch 7, flanges (not shown) extending outward from the open ends of the vertical walls 1 b of the square tubular component (bottomed container) can be provided at the same time in press forming, without generating strain based on bending deformation resistance in the ribs 1 g. 

1. A bottomed container comprising: a bottom portion; and a plurality of vertical walls rising from the peripheral edge of the bottom portion, wherein the bottomed container is formed by press-forming a blank, and has a plurality of corner portions integral with the bottom portion and the vertical walls adjacent to each other, the corner portions are each provided with one or more ribs that protrude outward or inward from between the vertical walls adjacent to each other in plan view, the ribs are each composed of a pair of folded flanges that are folded along creases that are preformed in the blank so as to substantially equally divide an area that will become one of the corner portions, the amount of outward or inward protrusion of the ribs becomes larger from the bottom portion toward the open end of the vertical walls in side view, and the ribs are provided with no flanges extending outward from the open ends of the ribs in plan view.
 2. The bottomed container according to claim 1, wherein the corner portions have a substantially arc shape in plan view, and the one or more ribs formed in each of the corner portions having a substantially arc shape are two to four ribs.
 3. The bottomed container according to claim 2, wherein recesses or protrusions that are continuous in plan view and that correspond to the ribs protruding outward or inward from the corner portions having a substantially arc shape are formed in the bottom portion.
 4. The bottomed container according to claim 3, wherein the recesses or protrusions provided in the bottom portion are formed so as to extend radially from the center of each of the corner portions having a substantially arc shape in plan view.
 5. The bottomed container according to claim 1, wherein the bottomed container is provided with flanges extending outward from the open ends of the vertical walls.
 6. A method for manufacturing the bottomed container according to claim 1, the method comprising: a preforming step comprising forming creases in a blank having areas that will become the bottom portion, the plurality of vertical walls, and the plurality of corner portions of the bottomed container after press forming using a preforming die, the creases being formed at borders between an area that will become the bottom portion and areas that will become the vertical walls, borders between the areas that will become the vertical walls and areas that will become the corner portions, and positions for substantially equally dividing the areas that will become the corner portions; and a main forming step comprising setting the blank, in which creases are formed by the preforming step, between a die and a punch such that the die and the punch correspond to the shape of the blank, and press-forming said blank to form the bottomed container, wherein in the main forming step, when one or more ribs protruding outward from between each adjacent two of the vertical walls of the bottomed container in plan view are formed in press forming, slits are provided in corner portions of the die, and when one or more ribs protruding inward from between each adjacent two of the vertical walls of the bottomed container in plan view are formed in press forming, slits are provided in corner portions of the outer side surface of the punch.
 7. The method for manufacturing a bottomed container according to claim 6, wherein in the preforming step, the number of creases formed for substantially equally dividing each of the areas that will become the corner portions is three to seven.
 8. The method for manufacturing a bottomed container according to claim 6, wherein the inside of each of the corner portions of the die is formed such that the radius of curvature of the inscribed circle is R1 in plan view, the corner portions of the outer side surface of the punch are formed in a shape having a curved surface having a radius of curvature of R2 in plan view corresponding to the inscribed circle of each of the corner portions of the die, the clearance between the punch and the die defined as R1−R2 is set to 100% to 200% of the thickness of the blank, and R1>R2.
 9. The method for manufacturing a bottomed container according to claim 8, wherein in the main forming step, when one or more ribs protruding outward from between each adjacent two of the vertical walls of the bottomed container in plan view are formed in press forming, slits are provided in the corner portions of the bottom surface of the die, and when one or more ribs protruding inward from between each adjacent two of the vertical walls of the bottomed container in plan view are formed in press forming, slits are provided in the corner portions of the bottom surface of the punch.
 10. The method for manufacturing a bottomed container according to claim 9, wherein the slits provided in the corner portions of the bottom surface of the die or the corner portions of the bottom surface of the punch are formed so as to extend radially from the center of each corner portion.
 11. The method for manufacturing a bottomed container according to claim 6, wherein flanges extending outward from the outer side surface other than the corner portions of the punch are provided at the upper end of the punch. 